1. Field of the Invention
The invention relates to a fluid pressure control circuit. More particularly, the invention relates to a technology for enhancing performance of supplying fluid to/discharging fluid from a fluid pressure device.
2. Description of the Related Art
A fluid pressure control circuit including a fluid pressure device and a control valve is used, for example, in a transmission for a vehicle. The fluid pressure device is operated by a fluid pressure. The control valve includes a supply/discharge port through which the fluid is supplied/discharged, and a communication port which is connected to the fluid pressure device through a communication passage. The control valve controls the fluid pressure of the fluid pressure device by changing a flow amount of the fluid to be supplied to or to be discharged from the fluid pressure device through the communication port and the supply/discharge port, the flow amount of the fluid being changed by the change in the state of communication (hereinafter, referred to as the “communication state”) between the communication port and the supply/discharge port according to the movement of a valve element, the movement of the valve element being determined by a ratio between i) the fluid pressure to be introduced from the communication passage into a feedback chamber and ii) a predetermined pressure regulating load. An example of such a fluid pressure control circuit is a hydraulic control circuit disclosed in Japanese Patent Laid-Open Publication No. JP-A-05-196127. The hydraulic control circuit includes a control valve which is provided with a supply port through which a fluid is supplied from an oil pump or the like, a discharge port through which the fluid is discharged, and a communication port to which the communication passage is connected. The control valve controls the fluid pressure by changing a flow amount of the fluid to be supplied to or to be discharged from the fluid pressure device, the flow amount of the fluid being changed by the communication state among the supply port, the discharge port and the communication port, the communication state being continuously changed according to a position of the valve element.
In such a fluid pressure control circuit, the fluid pressure of the fluid to be introduced from the communication passage to the feedback chamber does not always reflect the fluid pressure of the fluid pressure device due to the circulation resistance of the communication passage, which is caused when the fluid is being supplied/discharged or the fluid pressure is being changed. The fluid pressure in the feedback chamber is increased or decreased before the fluid pressure is changed. Accordingly, it is difficult to obtain sufficient responsiveness. If the fluid to be introduced to the feedback chamber is obtained at a position as close as possible to the fluid pressure device, the responsiveness is enhanced. However, when the supply of the fluid, the discharge of the fluid, or the change in the fluid pressure ends, that is, when a piston of a hydraulic cylinder reaches the end of the stroke, the fluid pressure may overshoot or undershoot. Also, fluctuation of the pressure (hereinafter, referred to as “pressure fluctuation”) is likely to occur due to the overshoot or the undershoot of the fluid pressure.